1. Field of the Invention
The invention relates to a gel dentifrice containing peroxide and a viscosity stabilization system.
2. The Related Art
Aqueous hydrogen peroxide is widely viewed by the dental profession as an effective treatment against gum disease. Periodontal disorders are believed to arise from infectious anaerobic microorganisms which are active in the absence of oxygen. These microorganisms can be controlled or entirely eliminated by contact with peroxides which release oxygen. According to this rationale, oxygen creates an aerobic atmosphere destructive to the microorganisms.
Facile reactivity of the peroxide benefits performance but conversely results in storage stability problems. Dentifrices containing peroxides tend to decompose within a relatively short period of time. Not only is activity lost but there can be a marked breakdown in the dentifrice's physical properties. Dentrifice viscosity is particularly adversely affected by the chemical breakdown of thickening agents. A variety of techniques have been developed to counter the problem. U.S. Pat. No. 4,226,851 (Sompayrac) discloses oral compositions comprising hydrogen peroxide and zinc chloride wherein vitamin E is added as a stabilizing agent. U.S. Pat. No. 4,788,052 and U.S. Pat. No. 4,839,157 both to Ng et al. report stable aqueous hydrogen peroxide gel dentifrices stabilized with a combination of hydrophilic and hydrophobic fumed silica. These gels include polyethylene glycol, sodium saccharin, sodium benzoate, polyethylene oxide type nonionic surfactant and flavor all maintained at a pH of 3-6, preferably 4.5-5, through acidification with phosphoric or citric acids. A related patent, U.S. Pat. No. 4,839,156 (Ng et al), further specifies use of polyoxyethylene-polyoxypropylene block copolymers, polyethylene glycol, nonionic surfactant and flavour. Again citric or phosphoric acids maintain a pH of about 4.5 to 6.
Stability may also be enhanced by employing relatively non-reactive components. For instance, U.S. Pat. No. 4,684,517, U.S. Pat. No. 4,537,778 and U.S. Pat. No. 4,431,631 all to Clipper et al report wintergreen and cinnamon flavors as being non-reactive in peroxide oral preparations. Other components include 1-20% polyhydric alcohols such as glycerol and up to 3% of polyoxyethylene-polyoxypropylene nonionic surfactants. Other patents such as U.S. Pat. No. 4,302,441 (Muhlemann et al) recommend that solid oral preparations comprising urea hydrogen peroxide be formulated without glycerol so as to be more effective against microorganisms on teeth. Glycerol was said to inhibit saliva and components thereof from beneficially decomposing the peroxide.
Oral compositions containing both a peroxide and sodium bicarbonate have been acclaimed by the dental profession, especially through the work of Keyes. See Keyes et al "Periodontics and Oral Hygiene", Jan. 1978, pages 51-56. Unfortunately, formulations based on the Keyes technology are particularly prone to decomposition. Several approaches have been reported to overcome difficulties presented by such combination of ingredients. U.S. Pat. No. 3,577,521 (Scheller) discloses use of acid salts in combination with alcohol-silica gels to obtain a foaming storage-stable toothpaste of peroxide-bicarbonate. U.S. Pat. No. 4,837,008 (Rudy et al) overcomes the problem through a non-aqueous dentifrice wherein an inorganic peroxide and/or bicarbonate is coated with a water-soluble barrier which is insoluble in the dentifrice vehicle.
U.S. Pat. No. 4,130,501 (Lutz) describes stable viscous hydrogen peroxide solutions formulated with Carbopol.RTM. thickener, a polyoxyethylene-polyoxypropylene surfactant and a neutralizing agent to raise pH between 4.5 and 8.
A physical separation into separate compartments of the peroxide from co-reactive ingredients has been another approach to the problem. U.S. Pat. No. 4,849,213 and U.S. Pat. No. 4,528,180 both to Schaeffer disclose a dual-compartment package with gel and paste components, respectively. The gel component includes hydrogen peroxide, a Carbopol.RTM. type thickener, a nonionic cellulose and a basic neutralizing agent with pH maintained at about 3-6.
U.S. Pat. No. 4,895,721 (Drucker) has focused both on the problem of viscosity and peroxide loss. Prevention of these problems is achieved through a gel base of 35-95% polyol (e.g. glycerol), and 0.75-5% gelling agent (e.g. Carbopol.RTM.), and 0.05-1% antioxidant or U.V. absorber with pH maintained at 3.5-6.5.
U.S. Pat. No. 4,343,785 (Schmolka) discloses a gel dentifrice containing a cogeneric mixture of polyoxybutylene-polyoxyethylene block copolymers (Pluronic.RTM. type) which may contain glycerol and be pH adjusted with citric acid. The combination is reported as retarding plaque formation and growth. The gel structure is retained even below 20.degree. C.
From all of the aforementioned art, it is apparent that hydrogen peroxide compositions should be formulated as simply as possible to minimize potential interactions between the peroxide and the remaining ingredients. Notwithstanding such precautions, gels can lose viscosity turning into the fluid state as temperature decreases. Except for U.S. Pat. No. 4,343,785, the literature has not appreciated that dental gels based on Pluronic.RTM. type formulations suffer from low temperature gel structure loss. This situation is rendered more difficult when a peroxide is formulated with the product. Even further difficulties arise where the peroxide gel is packaged within an expandable pump dispenser. At temperatures below 10.degree. C., gel consistency is lost, the product turns liquid and then leaks out of the dispenser.
Accordingly, it is an object of the present invention to provide a peroxide containing gel composition that maintains structure even at temperatures below 10.degree. C.
A further objective of the present invention is to provide a peroxide containing gel composition which under low temperature conditions remains confined to a pump dispenser package.
Another object of the present invention is to provide a gel composition of exceptional clarity.
A still further objective of the present invention is to achieve all of the above in combination with retaining a high peroxide stability.
These and other objects of the present invention will become more readily apparent upon consideration of the more detailed description and Examples which follow.